HELP! Jonsered CS 2252 Low Compression

[Excaliburrr]

Greetings, I have a Jonsered CS 2252 with low compression. To test I first could just tell by pulling it that it wasn't making enough compression at all, the compression release valve wouldn't even pop out. So I then preformed a compression test with a mityvac compression tester to verify my numbers and ended up with just a hair above 50psi with the air filter off, choke open, and W.O.T. I then poured a tiny amount of oil into the spark plug hole and turned the engine over a few times to spread it around inside the cylinder, then preformed a second compression test and got just under 100psi. This lead me to believe that either the piston/rings/cylinder are at fault. I have come to this conclusion as the oil that was poured into the cylinder has filled in any gaps or scoring on those components, thus allowing them to properly seal. To further verify this I took off the muffler and looked into the cylinder and the surface across from the exhaust looked pretty rough. I don't have any pictures at the moment as it's 10:00 P.M. and I'm not looking to dig into it right before bed. The only test I haven't preformed yet is a crankcase pressure/vacuum test as I don't have a tool for that. Given the information I've gotten so far would I be correct in saying that the piston/rings/cylinder are the issue? I would hate to spend the money on a new top end only for it to not be the solution.

 

[hacskaroly]

Given the information I've gotten so far would I be correct in saying that the piston/rings/cylinder are the issue? I would hate to spend the money on a new top end only for it to not be the solution.

Without pictures, but with your description, I would guess that there is scoring on the exhaust side with possible aluminum transfer onto the cylinder. During that process, it is likely some of the aluminum got smeared over the ring, preventing it from fully engaging the side. I would agree with you that the oil you put in, did likely seal enough to increase your pressure. Obviously popping off the cylinder and getting a better look at it and the piston/ring will give you a idea of what you will need. Likely piston and ring will be the minimum, and depending on the extent of the aluminum transfer onto the cylinder, you might get lucky and have minimal, enough to remove through various methods or have gouges too deep to fix needing a new cylinder.

I have two Husky 55s I am working on in the same boat, they both need new piston and rings, but I should be able to clean up the aluminum transfer to allow the cylinders to be reused.

 

[GMB74]

I agree with everything Hacskaroly has posted above.
You also must determine WHY this engine melted down and correct it or your repaired engine will do the same thing.
A pressure/vacuum test before the teardown will help you determine the cause. Then it can be corrected during your repairs instead of potentially having to tear the engine down a second time after assembly.
A p/v test after repair will insure that everything is airtight and proper and must be done to avoid a second meltdown.
The tools do not have to be expensive, a p/v tester from Harbor Freight and a piece of old tire inner tube or plumber's rubber gasket material from the hardware store will suffice. Search the pages here for more details.